Many methods have been developed to sense rotation and rotation rate. Gimbaled spinning wheels, ring lasers, and vibrating ring gyroscopes have all been successfully developed for this purpose. However, such existing gyroscope designs tend to be too expensive for many applications.
One prior art method of sensing rotation and rotation rate utilizes a vibrating mechanical element in which the Coriolis force that arises when the element is rotated is used to measure rotation rate. Devices of this type include the hemispherical resonator gyroscope and the vibrating ring gyroscope. Such vibratory gyroscopes have no rotating parts and are easily miniaturized using known micro-machining techniques. However, these gyroscopes tend to be very expensive.
Another method utilizes a rotation sensor based on a vibrating mechanical element, preferably a cantilever micro-beam, induced to laterally oscillate. In the prior art, such micro-beams are coupled directly to a stationary mounting structure. As the beam is vibrated, the vibration amplitude is measured by sensing the change in electrical capacitance between the moving beam and its stationary mounting structure. The magnitude of capacitance change is commonly on the order of femptofarads. As a result of such low capacitance levels, it becomes necessary to minimize the lead length connecting the beam with its associated measuring and control electronics so that the associated electronics must be fully integrated on the same chip as the micro-beam. This requirement is stressed in the published literature on the subject, such as: "Surface Micromachined Accelerometers" by B. E. Boser and R. T. Howe in IEEE Custom IC Conference, May 1995; and "A Surface Machined Silicon Accelerometer With On-Chip Detection Circuitry" by W. Kuehnel and S. Sherman in Elsevier Science Sensors and Actuators, 1994.
Further, considerable risk is involved in developing such a custom-designed, analog, integrated circuit in the absence of breadboard capability. Typically, more than one cycle of mask development, with its attendant costs, is required to produce the optimum configuration of the device.
However, there are situations where it is desirable to use the micro-beam gyroscope to utilize the "no wear-out" characteristics inherent in the device, but where less-than-maximum accuracy is required.
The present invention provides such a device along with compatibility with external breadboard electronics which, together with the relative simplicity of its electronics, eliminates the complex electronics, manufacture, and associated costs attendant with the prior art devices.